Thermal system with overshoot reduction

ABSTRACT

A thermal control unit for controlling a patient&#39;s temperature includes a fluid outlet for delivering temperature-controlled fluid to a patient, a pump, a heat exchanger, and a controller that automatically pauses thermal treatment of the patient prior the patient reaching a target temperature. During the pause, the controller assesses a reaction of the patient and changes a temperature of the fluid only inside the thermal control unit if the patient is likely to reach the target temperature without further thermal treatment. However, if the patient is unlikely to reach the target temperature without further thermal treatment, the controller restarts the thermal treatment. The controller may pause thermal treatment again prior to reaching the target temperature and assess the patient&#39;s reaction. In some embodiments, the controller may selectively include and exclude a fluid reservoir in a circulation channel within the thermal control unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationSer. No. 62/610,319 filed Dec. 26, 2017, by inventors Gregory S. Tayloret al. and entitled THERMAL SYSTEM WITH OVERSHOOT REDUCTION, thecomplete disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to a thermal control system forcontrolling the temperature of circulating fluid that is delivered toone or more thermal pads positioned in contact with a patient.

Thermal control systems are known in the art for controlling thetemperature of a patient by providing a thermal control unit thatsupplies temperature-controlled fluid to one or more thermal pads orcatheters positioned in contact with a patient. The thermal control unitincludes one or more heat exchangers for controlling the temperature ofthe fluid and a pump that pumps the temperature-controlled fluid to thepad(s) and/or catheter. After passing through the pad(s) and/orcatheter, the fluid is returned to the thermal control unit where anynecessary adjustments to the temperature of the returning fluid are madebefore being pumped back to the pad(s) and/or catheter. In someinstances, the temperature of the fluid is controlled to a static targettemperature, while in other instances the temperature of the fluid isvaried as necessary in order to automatically effectuate a targetpatient temperature.

The thermal control unit can be used to warm or cool a patient, and itis often desirable to heat or cool the patient to a target temperaturerelatively quickly. However, it is also often desirable to heat or coolthe patient to a target temperature without overshooting the targettemperature.

SUMMARY

The present disclosure is directed to an improved thermal control unitthat brings the patient's temperature to a target temperature in anexpeditious manner while also simultaneously reducing any overshoot inthe patient's temperature. By reducing such overshoot, the magnitude ofoscillations in the patient's temperature above and below a targettemperature may also be reduced, thereby enabling the patient'stemperature to be maintained within a tighter range of the targettemperature. In other aspects, the rate at which the temperature of thefluid circulating within the thermal control unit can be increased byselectively including and excluding a fluid reservoir in a circulationchannel within the thermal control unit. Still further, in otheraspects, the ease of carrying out disinfection of the thermal controlunit, including a fluid reservoir, may be improved. Still other improvedaspects of the thermal control system disclosed herein will be apparentto those skilled in the art in light of the following writtendescription.

According to one embodiment of the present disclosure a thermal controlunit is provided for controlling a patient's temperature that includes afluid outlet, a fluid inlet, a circulation channel, a pump, a heatexchanger, a fluid temperature sensor, a patient temperature probe port,a user interface, and a controller. The circulation channel is fluidlycoupled to the fluid outlet and fluid inlet. The pump circulates fluidthrough the circulation channel from the fluid inlet to the fluid outletand out of the fluid outlet. The heat exchanger adds or removes heatfrom the fluid circulating in the circulation channel when the heatexchanger is activated. The fluid temperature sensor senses atemperature of the circulating fluid. The patient temperature probe portreceives patient temperature readings from a patient temperature probe.The user interface receives a patient target temperature, and thecontroller stops a flow of fluid out of the fluid outlet prior to thepatient temperature reaching the patient target temperature.

According to other aspects of the present disclosure, the controllermonitors a slope of the patient temperature readings after the flow offluid out of the fluid outlet is stopped. The monitoring may continuefor a predefined time period. If the slope of the patient temperaturereadings changes by more than a threshold during the predefined timeperiod, the controller restarts the flow of fluid out of the fluidoutlet after the predefined time period. If the slope of the patienttemperature readings does not change by more than a threshold during thepredefined time period, the controller activates the pump and closes avalve such that the fluid circulates within the circulation channel ofthe thermal control unit but does not flow out of the fluid outlet.

The controller may activate the heat exchanger while the valve is closeduntil the temperature of the fluid reaches a specific temperature. Thespecific temperature may have a predefined relationship to a temperatureof the patient, and the controller may open the valve after thetemperature of the fluid reaches the specific temperature.

After restarting the flow of fluid out of the fluid outlet, thecontroller re-stops the flow of fluid out of the fluid outlet after thepatient temperature has moved toward the patient target temperature butprior to the patient temperature reaching the patient targettemperature.

In some embodiments, the controller stops the flow of fluid out of thefluid outlet by closing a valve to the fluid outlet, and the controllercontinues to activate the pump such that fluid is pumped internallywithin the circulation channel while the flow of fluid out of the fluidoutlet is stopped. In other embodiments, the controller may stop theflow of fluid out of the fluid outlet by deactivating the pump.

According to another embodiment, a thermal control unit for controllinga patient's temperature is provided that includes a fluid outlet, afluid inlet, a circulation channel, a pump, a heat exchanger, a fluidtemperature sensor, a patient temperature probe port, a user interface,and a controller. The pump circulates fluid through the circulationchannel from the fluid inlet to the fluid outlet and out of the fluidoutlet. The heat exchanger adds or removes heat from the fluidcirculating in the circulation channel when activated. The fluidtemperature sensor senses a temperature of the circulating fluid. Thepatient temperature probe port receives patient temperature readingsfrom a patient temperature probe. The user interface receives a patienttarget temperature, and the controller communicates with the temperatureprobe port, the pump, the fluid temperature sensor, and the userinterface. The controller is adapted to deactivate the heat exchangerprior to the patient temperature reaching the patient target temperaturesuch that the heat exchanger does not actively add heat to, or removeheat from, the circulating fluid.

After deactivating the heat exchanger, the controller monitors a slopeof the patient temperature readings for a predefined time period. Thecontroller reactivates the heat exchanger after the predefined timeperiod if the slope of the patient temperature readings changes by morethan a threshold. Thereafter, the controller may once again deactivatethe heat exchanger after the patient temperature has moved toward thepatient target temperature but prior to the patient temperature reachingthe patient target temperature.

If the slope of the patient temperature readings does not change by morethan a threshold during the predefined time period, the controller, insome embodiments, activates the pump and closes a valve such that thefluid circulates within the circulation channel of the thermal controlunit but does not flow out of the fluid outlet. The controller mayreactivate the heat exchanger while the valve is closed until thetemperature of the fluid reaches a specific temperature. The controlleropens the valve after the temperature of the fluid reaches the specifictemperature.

According to another embodiment of the present disclosure, a thermalcontrol unit for controlling a patient's temperature is provided. Thethermal control unit includes a fluid outlet, a fluid inlet, acirculation channel, a pump, a heat exchanger, a fluid temperaturesensor, a patient temperature probe port, a user interface, and acontroller. The pump circulates fluid through the circulation channelfrom the fluid inlet to the fluid outlet and out of the fluid outlet.The heat exchanger adds or removes heat from the fluid circulating inthe circulation channel when activated. The fluid temperature sensorsenses a temperature of the circulating fluid. The patient temperatureprobe port receives patient temperature readings from a patienttemperature probe. The user interface receives a patient targettemperature, and the controller communicates with the temperature probeport, the pump, the fluid temperature sensor, and the user interface.The controller is adapted to vary both a flow and temperature of thefluid exiting the fluid outlet in order to automatically bring thepatient to the patient target temperature.

In some embodiments, the controller reduces a flow of the fluid out ofthe fluid outlet prior to the patient temperature reaching the patienttarget temperature.

In some embodiments, the heat exchanger includes a compressor and thecontroller is further adapted to vary a speed of the compressor in orderto automatically bring the patient to the patient target temperature.

The controller may be adapted to vary a flow of the fluid exiting thefluid outlet by reducing the fluid flow or completely stopping the flowof fluid out of the fluid outlet.

When stopping the fluid flow, the controller may monitor a slope of thepatient temperature readings for a predefined time period and (1) if theslope of the patient temperature readings changes by more than athreshold during the predefined time period, the controller restarts theflow of fluid out of the fluid outlet; and (2) if the slope of thepatient temperature readings does not change by more than the thresholdduring the predefined time period, the controller activates the pump andcloses a valve such that the fluid circulates within the circulationchannel of the thermal control unit but does not flow out of the fluidoutlet.

In some embodiments, the thermal control unit includes a fluid reservoirand a valve adapted to selectively include and exclude the fluidreservoir to and from the circulation channel. The controller is adaptedto control the valve in order to automatically bring the patient to thepatient target temperature.

According to another embodiment of the present disclosure, a thermalcontrol unit for controlling a patient's temperature is provided. Thethermal control unit includes a fluid outlet, a fluid inlet, acirculation channel, a pump, a heat exchanger, a fluid reservoir, avalve, and a controller. The pump circulates fluid through thecirculation channel from the fluid inlet to the fluid outlet and out ofthe fluid outlet. The heat exchanger adds or removes heat from the fluidcirculating in the circulation channel when activated. The fluidreservoir supplies fluid to the circulation channel. The valveselectively includes the fluid reservoir in the circulation channel andselectively excludes the fluid reservoir from the circulation channel.When the reservoir is included in the circulation channel, thecirculating fluid flows through the reservoir. When the reservoir isexcluded from the circulation channel, the fluid flows around thereservoir. The controller communicates with the pump, the heatexchanger, and the valve, and the controller is adapted to control thevalve and the heat exchanger in order to automatically bring the patientto a patient target temperature.

According to other aspects of the disclosure, the controller controlsthe valve such that the fluid reservoir is included in the circulationchannel when the thermal control unit is being disinfected.

The controller, in some embodiments, controls the valve in combinationwith the heat exchanger in order to automatically bring the patient tothe patient target temperature.

In some embodiments, the controller controls the valve to exclude thefluid reservoir from the circulation channel for an initial periodduring which the patient temperature readings approach, but do notreach, the patient target temperature. During a subsequent time period,the controller controls the valve to include the fluid reservoir in thecirculation channel. The subsequent period may commence prior to thepatient reaching the patient target temperature.

The controller is configured in some embodiments to control the valvesuch that the fluid reservoir is included in the circulation channelwhen a quick increase in the temperature of the circulating fluid willreduce overshoot of the patient temperature readings past the patienttarget temperature.

According to another embodiment of the present disclosure, a thermalcontrol unit for controlling a patient's temperature is provided. Thethermal control unit includes a fluid outlet, a fluid inlet, acirculation channel, a pump, a heat exchanger, and a controller. Thepump circulates fluid through the circulation channel from the fluidinlet to the fluid outlet and out of the fluid outlet. The heatexchanger adds or removes heat from the fluid circulating in thecirculation channel when activated. The fluid reservoir supplies fluidto the circulation channel. The controller communicates with the pumpand heat exchanger and controls the heat exchanger to cool the patientto a target patient temperature. The controller is further adapted toautomatically pause the cooling of the patient prior to the patientreaching the target patient temperature and assess a reaction of thepatient to the paused cooling. The controller is still further adaptedto warm the circulating fluid internally within the thermal control unitif the reaction indicates the patient will likely reach the targetpatient temperature without further cooling by the thermal control unitand to restart cooling of the patient if the reaction of the patientindicates the patient will likely not reach the target patienttemperature without further cooling by the thermal control unit.

The pause in the cooling of the patient may be implemented by any one ormore of the following: deactivating the pump; keeping the pump activatedwhile closing a valve such that fluid does not exit out of the fluidoutlet; and/or deactivating the heat exchanger.

In some embodiments, the thermal control unit includes a fluid reservoiradapted to supply fluid to the circulation channel and a valve adaptedto selectively include the fluid reservoir in the circulation channeland selectively exclude the fluid reservoir from the circulationchannel. The fluid flows through the reservoir when the reservoir isincluded in the circulation channel and the fluid flows around thereservoir when the fluid reservoir is excluded from the circulationchannel.

The controller may control the valve such that the fluid reservoir isexcluded from the circulation channel during cooling of the patient.

The controller may control the valve such that the fluid reservoir isincluded in the circulation channel when the controller warms thecirculating fluid internally within the thermal control unit. Thecontroller, in some embodiments, includes the fluid reservoir in thecirculation channel for a predefined period when warming the circulationfluid internally within the thermal control unit and, after theexpiration of the predefined period, excludes the fluid reservoir fromthe circulation channel. The predefined period may be set equal to anamount of time it takes to pump a volume of fluid through the fluidreservoir substantially equal to the volume of the fluid that wascontained within the fluid reservoir immediately prior to the fluidreservoir being included in the circulation channel. In this manner, thefluid reservoir is included in the circulation channel for a length oftime sufficient to allow the fluid it contained prior to being includedin the circulation channel to be added to the circulation channel.

In some embodiments, the controller controls the heat exchanger usingfirst and second control loop feedback mechanisms. The first controlloop feedback mechanism uses a first set of coefficients and an errorvalue, and the second control loop feedback mechanism uses a second setof coefficients and the error value. The error value is defined as adifference between a current patient temperature reading and the patienttarget temperature.

According to another embodiment of the present disclosure, a thermalcontrol unit is provided for controlling a patient's temperature thatincludes a fluid outlet, a fluid inlet, a circulation channel, a pump, aheat exchanger, a fluid temperature sensor, a patient temperature probeport, a user interface, and a controller. The circulation channel isfluidly coupled to the fluid outlet and fluid inlet. The pump circulatesfluid through the circulation channel from the fluid inlet to the fluidoutlet and out of the fluid outlet. The heat exchanger adds or removesheat from the fluid circulating in the circulation channel when the heatexchanger is activated. The fluid temperature sensor senses atemperature of the circulating fluid. The patient temperature probe portreceives patient temperature readings from a patient temperature probe.The user interface receives a patient target temperature and thecontroller communicates with the temperature probe port, the pump, theheat exchanger, the fluid temperature sensor, and the user interface.The controller controls the heat exchanger to bring the patient to thepatient target temperature using first and second control loop feedbackmechanisms. The first control loop feedback mechanism uses a first setof coefficients and an error value, and the second control loop feedbackmechanism uses a second set of coefficients and the error value. Theerror value is defined as a difference between a current patienttemperature reading and the patient target temperature.

In some of the aforementioned embodiments, the first control loopfeedback mechanism includes first proportional, first integral, andfirst derivative control terms, each of which is multiplied by acoefficient from the first set of coefficients; and the second controlloop feedback mechanism includes second proportional, second integral,and second derivative control terms, each of which is multiplied by acoefficient from the second set of coefficients. In still otherembodiments, the set of coefficients includes fewer than threecoefficients.

The controller switches from using the first control loop feedbackmechanism to using the second control loop feedback mechanism at atransition point. The transition point occurs prior to the patientreaching the patient target temperature in some embodiments. In otherembodiments, the transition point occurs after the patient reaches thepatient target temperature.

In still other embodiments, the controller is further adapted to controlthe heat exchanger to bring the patient to the patient targettemperature using a third control loop feedback mechanism. The thirdcontrol loop feedback mechanism uses a third set of coefficients and theerror value. The controller switches from using the second control loopfeedback mechanism to using the third control loop feedback mechanism ata second transition point. The second transition point occurs afterfirst transition point.

In any of the embodiments disclosed herein, the fluid reservoir may bethermally isolated from the heat exchanger when the fluid reservoir isnot in the circulation channel, thereby allowing the fluid in thereservoir to have a different temperature than the fluid in thecirculation channel. When the fluid reservoir is brought into thecirculation channel, the fluid from the reservoir mixes with the fluidin the circulation channel and the temperature of the circulating fluidis changed based on the temperature of the fluid from the reservoir andthe volume of fluid that exits from the reservoir and into thecirculation channel.

Before the various embodiments disclosed herein are explained in detail,it is to be understood that the claims are not to be limited to thedetails of operation or to the details of construction, nor to thearrangement of the components set forth in the following description orillustrated in the drawings. The embodiments described herein arecapable of being practiced or being carried out in alternative ways notexpressly disclosed herein. Also, it is to be understood that thephraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. Further, enumeration may beused in the description of various embodiments. Unless otherwiseexpressly stated, the use of enumeration should not be construed aslimiting the claims to any specific order or number of components. Norshould the use of enumeration be construed as excluding from the scopeof the claims any additional steps or components that might be combinedwith or into the enumerated steps or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a thermal control system according toone aspect of the present disclosure shown applied to a patient on apatient support apparatus;

FIG. 2 is a perspective view of a thermal control unit of the thermalcontrol system of FIG. 1;

FIG. 3 is a block diagram of a first embodiment of the thermal controlunit of FIG. 2;

FIG. 4 is an illustrative control loop diagram that may be incorporatedinto at least one embodiment of the thermal control unit of FIG. 3;

FIG. 5 is a flow diagram of a first temperature control algorithm thatmay be followed by a controller of the thermal control unit of FIG. 3;

FIG. 6 is a graph of a patient target temperature, patient measuredtemperature, and fluid temperature illustrating a first example of thetemperature control algorithm of FIG. 5;

FIG. 7 is a graph of a patient target temperature, patient measuredtemperature, and fluid temperature illustrating a second example of thetemperature control algorithm of FIG. 5;

FIG. 8 is a flow diagram of a second temperature control algorithm thatmay be followed by a controller of the thermal control unit of FIG. 3;

FIG. 9 is a block diagram of a second embodiment of the thermal controlunit of FIG. 2;

FIG. 10 is a flow diagram of a third temperature control algorithm thatmay be followed by a controller of the thermal control unit of FIG. 9;

FIG. 11 is a flow diagram of a fourth temperature control algorithm thatmay be followed by a controller of the thermal control unit of FIG. 9;and

FIG. 12 is a graph of patient target temperature, patient measuredtemperature, and fluid temperature illustrating an example of a fifthtemperature control algorithm that may be followed by the thermalcontrol units of FIG. 3 and/or FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A thermal control system 20 according to one embodiment of the presentdisclosure is shown in FIG. 1. Thermal control system 20 is adapted tocontrol the temperature of a patient 28, which may involve raising,lowering, and/or maintaining the patient's temperature. Thermal controlsystem 20 includes a thermal control unit 22 coupled to one or morethermal therapy devices 24. The thermal therapy devices 24 areillustrated in FIG. 1 to be thermal pads, but it will be understood thatthermal therapy devices 24 may take on other forms, such as, but notlimited to, blankets, vests, patches, caps, catheters, or otherstructures that receive temperature-controlled fluid. For purposes ofthe following written description, thermal therapy devices 24 will bereferred to as thermal pads 24, but it will be understood by thoseskilled in the art that this terminology is used merely for convenienceand that the phrase “thermal pad” is intended to cover all of thedifferent variations of thermal therapy devices 24 mentioned above (e.g.blankets, vests, patches, caps, catheters, etc.) and variations thereof.

Thermal control unit 22 is coupled to thermal pads 24 via a plurality ofhoses 26. Thermal control unit 22 delivers temperature-controlled fluid(such as, but not limited to, water or a water mixture) to the thermalpads 24 via the fluid supply hoses 26 a. After thetemperature-controlled fluid has passed through thermal pads 24, thermalcontrol unit 22 receives the temperature-controlled fluid back fromthermal pads 24 via the return hoses 26 b.

In the embodiment of thermal control system 20 shown in FIG. 1, threethermal pads 24 are used in the treatment of patient 28. A first thermalpad 24 is wrapped around a patient's torso, while second and thirdthermal pads 24 are wrapped, respectively, around the patient's rightand left legs. Other configurations can be used and different numbers ofthermal pads 24 may be used with thermal control unit 22, depending uponthe number of inlet and outlet ports that are included with thermalcontrol unit 22. By controlling the temperature of the fluid deliveredto thermal pads 24 via supply hoses 26 a, the temperature of the patient28 can be controlled via the close contact of the pads 24 with thepatient 28 and the resultant heat transfer therebetween.

As shown more clearly in FIG. 2, thermal control unit 22 includes a mainbody 30 to which a removable reservoir 32 may be coupled and uncoupled.Removable reservoir 32 is configured to hold the fluid that is to becirculated through control unit 22 and the one or more thermal pads 24.By being removable from thermal control unit 22, reservoir 32 can beeasily carried to a sink or faucet for filling and/or dumping of thewater or other fluid. This allows users of thermal control system 20 tomore easily fill control unit 22 prior to its use, as well as to drainunit 22 after use.

As shown in FIG. 3, thermal control unit 22 includes a pump 34 forcirculating fluid through a circulation channel 36. Pump 34, whenactivated, circulates the fluid through circulation channel 36 in thedirection of arrows 38 (clockwise in FIG. 3). Starting at pump 34 thecirculating fluid first passes through a heat exchanger 40 that adjusts,as necessary, the temperature of the circulating fluid. Heat exchanger40 may take on a variety of different forms. In some embodiments, heatexchanger 40 is a thermoelectric heater and cooler. In the embodimentshown in FIG. 3, heat exchanger 40 includes a chiller 41 and a heater43. Further, in the embodiment shown in FIG. 3, chiller 41 is aconventional vapor-compression refrigeration unit having a compressor45, a condenser 47, an evaporator 49, an expansion valve (not shown),and a fan 51 for removing heat from the condenser. Other types ofchillers and/or heaters may be used.

After passing through heat exchanger 40, the circulating fluid isdelivered to an outlet manifold 42 having an outlet temperature sensor44 and a plurality of outlet ports 46. Temperature sensor 44 is adaptedto detect a temperature of the fluid inside of outlet manifold 42 andreport it to a controller 66. Outlet ports 46 are coupled to supplyhoses 26 a. Supply hoses 26 a are coupled, in turn, to thermal pads 24and deliver temperature-controlled fluid to the thermal pads 24. Thetemperature-controlled fluid, after passing through the thermal pads 24,is returned to thermal control unit 22 via return hoses 26 b. Returnhoses 26 b couple to a plurality of inlet ports 48. Inlet ports 48 arefluidly coupled to an inlet manifold 50 inside of thermal control unit22.

Control unit 22 also includes a bypass line 52 fluidly coupled to outletmanifold 42 and inlet manifold 50 (FIG. 3). Bypass line 52 allows fluidto circulate through circulation channel 36 even in the absence of anythermal pads 24 or hoses 26 a being coupled to any of outlet ports 46.In the illustrated embodiment, bypass line 52 includes an optionalfilter 54 that is adapted to filter the circulating fluid. If included,filter 54 may be a particle filter adapted to filter out particleswithin the circulating fluid that exceed a size threshold, or filter 54may be a biological filter adapted to purify or sanitize the circulatingfluid, or it may be a combination of both. In some embodiments, filter54 is constructed and/or positioned within thermal control unit 22 inany of the manners disclosed in commonly assigned U.S. patentapplication Ser. No. 62/404,676 filed Oct. 11, 2016, by inventors MarkoKostic et al. and entitled THERMAL CONTROL SYSTEM, the completedisclosure of which is incorporated herein by reference.

The flow of fluid through bypass line 52 is controllable by way of abypass valve 56 positioned at the intersection of bypass line 52 andoutlet manifold 42 (FIG. 3). When open, bypass valve 56 allows fluid toflow through circulation channel 36 to outlet manifold 42, and fromoutlet manifold 42 to the connected thermal pads 24. When closed, bypassvalve 56 stops fluid from flowing to outlet manifold 42 (and thermalpads 24) and instead diverts the fluid flow along bypass line 52. Insome embodiments, bypass valve 56 may be controllable such thatselective portions of the fluid are directed to outlet manifold 42 andalong bypass line 52. As will be discussed in more detail below, thestopping of fluid flow to thermal pads 24 via bypass valve 56 may occurduring the thermal treatment of a patient, as well as at other times.

The incoming fluid flowing into inlet manifold 50 from inlet ports 48and/or bypass line 52 travels back toward pump 34 and into an airremover 58. Air remover 58 includes any structure in which the flow offluid slows down sufficiently to allow air bubbles contained within thecirculating fluid to float upwardly and escape to the ambientsurroundings. In some embodiments, air remover 58 is constructed inaccordance with any of the configurations disclosed in commonly assignedU.S. patent application Ser. No. 15/646,847 filed Jul. 11, 2017, byinventor Gregory S. Taylor and entitled THERMAL CONTROL SYSTEM, thecomplete disclosure of which is hereby incorporated herein by reference.After passing through air remover 58, the circulating fluid flows past avalve 60 positioned beneath fluid reservoir 32. Fluid reservoir 32supplies fluid to thermal control unit 22 and circulation channel 36 viavalve 60, which may be a conventional check valve, or other type ofvalve, that automatically opens when reservoir 32 is coupled to thermalcontrol unit 22 and that automatically closes when reservoir 32 isdecoupled from thermal control unit 22 (see FIG. 2). After passing byvalve 60, the circulating fluid travels to pump 34 and the circuit isrepeated.

Controller 66 of thermal control unit 22 is contained within main body30 of thermal control unit 22 and is in electrical communication withpump 34, heat exchanger 40, outlet temperature sensor 44, bypass valve56, a patient temperature module 62, and a user interface 64. Controller66 includes any and all electrical circuitry and components necessary tocarry out the functions and algorithms described herein, as would beknown to one of ordinary skill in the art. Generally speaking,controller 66 may include one or more microcontrollers, microprocessors,and/or other programmable electronics that are programmed to carry outthe functions described herein. It will be understood that controller 66may also include other electronic components that are programmed tocarry out the functions described herein, or that support themicrocontrollers, microprocessors, and/or other electronics. The otherelectronic components include, but are not limited to, one or more fieldprogrammable gate arrays, systems on a chip, volatile or nonvolatilememory, discrete circuitry, integrated circuits, application specificintegrated circuits (ASICs) and/or other hardware, software, orfirmware, as would be known to one of ordinary skill in the art. Suchcomponents can be physically configured in any suitable manner, such asby mounting them to one or more circuit boards, or arranging them inother manners, whether combined into a single unit or distributed acrossmultiple units. Such components may be physically distributed indifferent positions in thermal control unit 22, or they may reside in acommon location within thermal control unit 22. When physicallydistributed, the components may communicate using any suitable serial orparallel communication protocol, such as, but not limited to, CAN, LIN,Firewire, I-squared-C, RS-232, RS-465, universal serial bus (USB), etc.

User interface 64, which may be implemented as a control panel or inother manners, allows a user to operate thermal control unit 22. Userinterface 64 communicates with controller 66 and includes controls 68enabling a user to turn control unit 22 on and off, select a mode ofoperation, select a target temperature for the fluid delivered tothermal pads 24, select a patient target temperature, and control otheraspects of thermal control unit 22. In some embodiments, user interfacemay include a pause/event control, a medication control, and/or anautomatic temperature adjustment control that operate in accordance withthe pause event control 66 b, medication control 66 c, and automatictemperature adjustment control 66 d disclosed in commonly assigned U.S.patent application Ser. No. 62/577,772 filed on Oct. 27, 2017, byinventors Gregory Taylor et al. and entitled THERMAL SYSTEM WITHMEDICATION INTERACTION, the complete disclosure of which is incorporatedherein by reference.

In those embodiments where user interface 64 allows a user to selectfrom different modes for controlling the patient's temperature, thedifferent modes include, but are not limited to, a manual mode and anautomatic mode, both of which may be used for cooling and heating thepatient. In the manual mode, a user selects a target temperature for thefluid that circulates within thermal control unit 22 and that isdelivered to thermal pads 24. Control unit 22 then makes adjustments toheat exchanger 40 in order to ensure that the temperature of the fluidexiting supply hoses 26 a is at the user-selected temperature.

Another one of the modes is an automatic mode. When the user selects theautomatic mode, the user selects a target patient temperature, ratherthan a target fluid temperature. After selecting the target patienttemperature, controller 66 makes automatic adjustments to thetemperature of the fluid in order to bring the patient's temperature tothe desired patient target temperature. In this mode, the temperature ofthe circulating fluid may vary as necessary in order to bring about thetarget patient temperature.

In order to carry out the automatic mode, thermal control unit 22utilizes patient temperature module 62. Patient temperature module 62includes one or more patient temperature probe ports 70 (FIGS. 2 & 3)that are adapted to receive one or more conventional patient temperatureprobes 72. The patient temperature probes 72 may be any suitable patienttemperature probe that is able to sense the temperature of the patientat the location of the probe. In one embodiment, the patient temperatureprobes are conventional Y.S.I. 400 probes marketed by YSI Incorporatedof Yellow Springs, Ohio, or probes that are YSI 400 compliant. In otherembodiments, different types of probes may be used with thermal controlunit 22. Regardless of the specific type of patient temperature probeused in thermal control system 20, each temperature probe 72 isconnected to a patient temperature probe port 70 positioned on controlunit 22. Patient temperature probe ports 70 are in electricalcommunication with controller 66 and provide current temperaturereadings of the patient's temperature.

FIG. 4 illustrates a pair of feedback loops 74 a and 74 b that are usedin at least one embodiment of thermal control unit 22. Feedback loop 74a is used by controller 66 when thermal control unit 22 is operating inthe manual mode and feedback loops 74 a and 74 b are both used bycontroller 66 when thermal control unit 22 is operating in the automaticmode. Feedback loop 74 a uses a measured fluid temperature 76 and afluid target temperature 78 as inputs. Measured fluid temperature 76comes from outlet temperature sensor 44. Fluid target temperature 78,when thermal control unit 22 is operating in the manual mode, comes froma user inputting a desired fluid temperature using controls 68 of userinterface 64. When thermal control unit 22 is operating in the automaticmode, fluid target temperature 78 comes from the output of control loop74 b, as discussed more below.

Control loop 74 a determines the difference between the fluid targettemperature 78 and the measured fluid temperature 76 (T_(F)error) anduses the resulting error value as an input into a conventionalProportional, Integral, Derivative (PID) control loop. That is,controller 66 multiplies the fluid temperature error by a proportionalconstant (C_(P)) at step 80, determines the derivative of the fluidtemperature error over time and multiplies it by a constant (C_(D)) atstep 82, and determines the integral of the fluid temperature error overtime and multiplies it by a constant (C_(I)) at step 82. The results ofsteps 80, 82, and 84 are summed together and converted to aheating/cooling command at step 86. The heating/cooling command is fedto heat exchanger 40 and tells heat exchanger 40 whether to heat and/orcool the circulating fluid and how much heating/cooling power to use.

Control loop 74 b which, as noted, is used during the automatic mode,determines the difference between a patient target temperature 88 and ameasured patient temperature 90. Patient target temperature 88 is inputby a user of thermal control unit 22 using controls 68 of user interface64. Measured patient temperature 90 comes from a patient temperatureprobe 72 coupled to one of patient temperature probe ports 70 (FIG. 3).Controller 66 determines the difference between the patient targettemperature 88 and the measured patient temperature 90 (T_(P)error) anduses the resulting patient temperature error value as an input into aconventional PID control loop (FIG. 4). As part of the PID loop,controller 66 multiples the patient temperature error by a proportionalconstant (K_(P)) at step 92, multiplies a derivative of the patienttemperature error over time by a derivative constant (K_(D)) at step 94,and multiplies an integral of the patient temperature error over time byan integral constant (K_(I)) at step 96. The results of steps 92, 94,and 96 are summed together and converted to a target fluid temperaturevalue 78. The target fluid temperature value 78 is then fed to controlloop 74 a, which uses it to compute a fluid temperature error, asdiscussed above.

It will be understood by those skilled in the art that although FIG. 4illustrates two PID control loops 74 a and 74 b, other types of controlloops may be used, including, but not limited to, a single control loopor more than two control loops. As other examples, loops 74 a and/or 74b can be replaced by one or more PI loops, PD loops, and/or other typesof control equations. Controller 66 implements loops 74 a and/or 74 bmultiple times a second in at least one embodiment, although it will beunderstood that this rate may be varied widely. After controller 66 hasoutput a heat/cool command at step 86 to heat exchanger 40, controller66 takes another patient temperature reading 90 and/or another fluidtemperature reading 76 and re-performs loops 74 a and/or 74 b. Thespecific loop(s) used, as noted previously, depends upon whether thermalcontrol unit 22 is operating in the manual mode or automatic mode.

It will also be understood by those skilled in the art that the outputof the control loop 74 a may be limited such that the temperature of thefluid delivered to thermal pads 24 by thermal control unit 22 neverstrays outside of a predefined maximum and a predefined minimum. Thepredefined minimum temperature, an example of which is shown in FIG. 6and assigned the reference number 126, is a temperature below whichcontroller 66 does not lower the temperature of the circulating fluid.Minimum temperature 126 is designed as a safety temperature and mayvary. In some embodiments, it may be set to about four degrees Celsius,although other temperatures may be selected. The predefined maximumtemperature, an example of which is also shown in FIG. 6 and assignedreference number 128, is a temperature above which controller 66 doesnot heat the circulating fluid. The predetermined maximum temperature128 is also implemented as a safety measure and may be set to aboutforty degrees Celsius, although other values may be selected.

FIG. 5 illustrates in more detail a temperature control algorithm 98that controller 66 is adapted to implement in some embodiments ofthermal control unit 22. Temperature control algorithm 98 is implementedwhen thermal control unit 22 is operating in the automatic mode—that is,when thermal control unit 22 is heating and/or cooling the temperatureof the circulating fluid in order to automatically bring the temperatureof the patient to a target temperature, and/or to maintain the patienttemperature at the selected target temperature. Algorithm 98 begins at atemperature selection step 100 in which a user selects the patienttarget temperature 88.

After selecting the patient target temperature 88, controller 66 movesto step 102 where it takes readings of the basic variables used incontrolling the patient's temperature. These basic variables include thefluid temperature (measured by outlet temperature sensor 44), thepatient temperature 90 (as measured by a patient temperature probe 72),and the patient target temperature 88 (as input by a user). Inalternative embodiments, one or more additional readings may be taken,such as one or more measurements of the flow rate of fluid incirculation channel 36, a pump speed, a temperature of fluid returninginto inlet manifold 50, the amount of heat removed from, or added to,the patient, and/or other variables.

After taking readings of the basic variables at step 102, controller 66moves to step 104 where it implements the computations of control loops74 a and 74 b (FIG. 4). That is, controller 66 determines the currenterror between the patient's measured temperature 90 and the patienttarget temperature 88 and feeds these variables into control loop 74 b(FIG. 4). The output of control loop 74 b is a target fluid temperature78, which controller compares against the current fluid temperature 76to determine a fluid temperature error for use in control loop 74 a.After determining the fluid temperature error, controller 66 performssteps 80-84 and outputs a heating/cooling command at step 86 to heatexchanger 40.

After control loops 74 a and 74 b have been completed once (or more thanonce), controller 66 moves onto step 106 (FIG. 5). At step 106controller 66 determines whether a current patient temperature reading(T_(P)) taken from patient temperature probe 72 is equal to a thresholdtemperature T_(A). If the current patient temperature is not yet equalto the temperature threshold T_(A), controller 66 returns to step 102where it takes fresh readings of the patient temperature 90 and fluidtemperature 76 for use in repeating step 104 in the manner described. Ifthe current patient temperature is equal to the temperature thresholdT_(A) at step 106, controller 66 moves onto step 108, as will bediscussed more below.

The temperature threshold T_(A) used in step 106 is a temperature thatis intermediate the initial temperature of the patient (P_(I); FIG. 6)when algorithm 98 starts and the patient target temperature 88. In someembodiments, T_(A) is based on a specific patient temperature value,such as, but not limited to a patient temperature value that isapproximately half way between the patient's initial temperature (P_(I))and the patient's target temperature 88. Thus, for example, if thepatient's initial temperature is thirty-seven degrees Celsius and thetarget patient temperature is thirty-three degrees Celsius, T_(A) may beset equal to thirty-five degrees Celsius. In some embodiments, T_(A) isnot a temperature magnitude, but a slope magnitude that has to be met bythe slope of recent patient temperature readings 90 before controller 66moves onto step 108. In still other embodiments, T_(A) is based on acombination of the slope of the patient temperature readings and also aspecific patient temperature value. In these latter embodiments,controller 66 may look for a specific threshold slope to be achievedbefore then examining whether a specific temperature is achieved, orvice versa. Still other ways of combining a value and the rate of changeof that value may be used.

If controller 66 determines at step 106 (FIG. 5) that the patient'scurrent temperature is equal to T_(A) or has moved past T_(A),controller 66 moves to step 108. At step 108, controller 66 stops theflow of fluid to the thermal pads 24. Controller 66 may achieve thistermination of fluid flow in different manners. In one embodiment,controller 66 closes bypass valve 56 such that the fluid being pumped bypump 34 is diverted to bypass line 52 and does not exit out of outletports 46. In an alternative embodiment, controller 66 stops the fluidflow to thermal pads 24 by switching off pump 34. In either embodiment,controller 66 thereafter proceeds to step 110 and monitors the patienttemperature while the fluid flow to pads 24 has been temporarilyterminated.

At step 110 (FIG. 5), controller 66 determines how the patient'stemperature readings 90 react to the cessation of fluid to thermal pads24. Controller 66 determines this reaction over a predefined amount oftime, which may be on the order of several minutes or more, although avariety of different time periods may be used. Controller 66specifically measures and monitors changes in the slope of the patienttemperature readings 90 at step 110 while the flow of fluid isterminated to pads 24. Controller 66 monitors changes in the slope ofthe patient temperature readings 90 in order to assess whether thepatient's temperature will likely reach the patient target temperature88 within a desired time period without further fluid being supplied tothermal pads 24, or whether it is unlikely that the patient'stemperature will reach the patient target temperature 88 within thedesired time period without supplying additional fluid to thermal pads24. This assessment occurs at step 112, and the desired time period maybe set based upon the absolute value of T_(A), the difference betweenthe patient's current temperature and target temperature, and/or otherfactors.

At step 112, controller 66 determines whether the slope of the patienttemperature readings shallows out or not within the time period duringwhich the fluid flow is ceased. This assessment is based upon whether ornot the change in the slope of the temperature exceeds one or morethresholds. FIGS. 6 and 7 provide two examples of this assessment. InFIG. 6, the patient is being cooled from an initial patient temperatureP_(I) toward a target temperature P_(T). As shown therein, the patient'stemperature reaches point T_(A) at time T₁. Controller 66 thereforeturns off fluid flow to the thermal pads 24 at time T₁ in accordancewith step 108 of algorithm 98 (FIG. 5). From time T₁ to time T₂,controller 66 monitors the change in the patient's temperature 90 anddetermines whether the change in this temperature has shallowed out morethan a threshold or not, in accordance with steps 110 and 112 ofalgorithm 98.

In the particular example of FIG. 6, it can be seen that the slope ofthe patient temperature readings 90 has changed very little in theinterim between times T₁ and T₂ when compared with the slope of thepatient temperature readings 90 in the moments before T₁. That is, therate at which the patient's temperature was dropping in the momentsprior to time T₁ did not change much in the interim time period betweentimes T₁ and T₂. Accordingly, it is likely that the patient'stemperature will continue to drop sufficiently far to reach the targettemperature 88 without further fluid being delivered to thermal pads 24.Accordingly, controller 66 moves from step 112 to step 114.

At step 114 (FIG. 5), controller 66 closes bypass valve 56 (to theextent it wasn't already closed at step 108). Controller 66 then movesonto step 116 where it begins warming the circulating fluid towards ahigher temperature (such as, but not limited to, maximum temperature128, a temperature that is a predetermined amount above the patient'starget temperature, or another temperature). Controller 66 carries outthe warming at step 116 by starting pump 34 (if it was previouslystopped at step 108), or continuing to run pump 34 (if it was notpreviously stopped at step 108) and sending heating instructions to heatexchanger 40. During this time, because bypass valve 56 remains closed,the fluid inside of thermal control unit 22 circulates purely internallywithin thermal control unit 22 and circulation channel 36. Becausecirculation channel 36 passes through heat exchanger 40, this internalcirculation heats the fluid as it passes through heat exchanger 40.

The heating of fluid within thermal control unit 22 carried out duringstep 116 (FIG. 5) continues until time T₃ is reached (FIG. 6). Time T₃is the time at which the fluid temperature 76 meets or exceeds thecurrent patient temperature 90 and it corresponds to the time at whichstep 118 is carried out in FIG. 5. In the example illustrated in FIG. 6,time T₃ is the time at which the fluid temperature 76 exceeds thepatient temperature 90 by one degree Celsius. At time T₃, controller 66opens bypass valve 56 so that the circulating fluid is able to flow tooutlet manifold 42, which in turn delivers the fluid to thermal pads 24.Accordingly, at time T₃, the warmed fluid is delivered to the patient.

This warmed fluid is delivered to the patient at time T₃ in order toprevent overshoot of the patient's temperature. In the specific exampleof FIG. 6, the warmed fluid is delivered to the patient slightly priorto the patient's temperature reaching the target temperature 88. In theabsence of the delivery of the warmed fluid, the patient's temperaturewould likely continue downward and past the target temperature to agreater extent than the overshoot illustrated (T_(over)). Accordingly,by delivering the warmed fluid to thermal pads 24 prior to reaching thetarget temperature, the rate of the patient's temperature drop can beslowed to close to zero at or near the moment the patient reaches thetarget temperature. In this manner, the patient's target temperature isreached more quickly, but with reduced overshoot.

During the warming of the fluid between time T₂ and T₃, controller 66may take and analyze additional readings of the patient's temperature tosee if the patient's temperature is continuing to move toward the targettemperature 88. In the event the patient's progress toward targettemperature 88 stalls or stops, controller 66 may be programmed to carryout step 118 (open bypass valve 56) sooner or later than it otherwisewould (depending on the current temperature of the fluid in thermalcontrol unit 22) if supplying the fluid at its current temperature tothe thermal pads 24 would help advance the patient's progress towardtarget temperature 88. Controller 66 may therefore determine time T₃ insome embodiments by calculating the difference between the patient'stemperature 90 and the target temperature 88 and/or by calculating theslope of the patient's temperature 90. These calculations may be doneeither in lieu of or in addition to the aforementioned comparison of thefluid temperature to the patient's temperature. In other words, T₃ maybe defined strictly on a comparison between the current fluidtemperature and patient temperature, or it may be defined based on theslope of the patient's temperature, or it may be defined on the distancebetween the patient's temperature 90 and the target temperature 88, or acombination of any of these.

As a result, if the patient is taking longer to reach target temperature88 than was anticipated by controller 66 at time T₁, controller 66 maydelay the delivery of warm fluid to the thermal pads past the moment thefluid temperature is equal to, or more than one degree Celsius above,the patient's temperature. In this manner, the delivery of the warmfluid is delayed so that it doesn't cause the patient's temperature topossibly not reach the target temperature 88. Alternatively, oradditionally, controller 66 may expedite the delivery of warm fluid tothe thermal pads 24 prior to the moment the fluid temperature is equalto, or more than one degree above, the patient's temperature. Suchexpediting is performed if the patient's temperature drops faster thancontroller 66 had anticipated at time T₁.

With respect to FIG. 6, controller 66 uses the control loops 74 a and 74b to control the temperature of the circulating fluid between thebeginning of thermal therapy (time T₀) and time T₁. Between time T₁ andT₂, controller 66 may deactivate the heat exchanger, or it may continueto control the temperature of the fluid using control loops 74 a and 74b, or it may control the heat exchanger 40 in another matter. Differentembodiments may select different ones of these options. The differentoptions are available because during the time period from T₁ to T₂,fluid is not being delivered to the patient, so the precise manner inwhich the fluid temperature is controlled is not critical. In the timeperiod between T₂ and T₃, controller 66 may use control loop 74 a (withthe target fluid temperature set to a maximum or to a predeterminedamount above the patient target temperature 88) to heat the fluid, or itmay use open loop heating. After time T₃, controller 66 switches back tousing control loops 74 a and 74 b (to the extent it hasn't switched backearlier).

One of the reasons why controller 66 stops deliveringtemperature-controlled fluid to the thermal pads 24 at time T₂ isbecause the temperature reaction of patients to the thermal treatmentvaries from individual patient to individual patient. It can thereforebe difficult to tune a PID (or other type) of control loop to change anindividual patient's temperature in the most efficient manner withoutovershoot. By stopping the delivery of fluid to the patient, however,controller 66 is able to assess the individual temperature response ofthe particular patient undergoing thermal treatment at that time. Thisindividual assessment allows for control of the temperature of thecirculating fluid that is more specifically tailored to the individualundergoing thermal treatment. Without this individually tailoredcontrol, the PID control loops 74 a and 74 b (or other types of controlloops) may not start warming patient until the patient temperaturereaches target temperature 88, or only a short time period before then.In either case, due to the amount of time it takes to warm the fluid,fluid will likely be delivered to the patient that is below the targettemperature 88 after the patient has already reached target temperature88, which will likely further exacerbate the overshoot.

Returning to FIG. 5, after controller 66 opens bypass valve 56 at step118, controller 66 moves to step 120 and calculates a new time T_(A) atstep 122. The calculation of a new time T_(A) at step 120 is an optionalstep. In some embodiments, algorithm 98 includes step 120, while inother embodiments, algorithm 98 does not include step 120. Whenalgorithm 98 does not include step 120, controller 66 returns tocontrolling the temperature of the fluid using control loops 74 a and 74b for the remainder of the thermal treatment session. When algorithm 98does include step 120, controller 66 calculates a new T_(A) value inorder to help future overshoot on the opposite side of the patient'starget temperature 88. In other words, the repetition of steps 100-118via step 120 is designed to reduce overshoot after the patient'stemperature reaches the target temperature the second time (or a thirdtime, a fourth time, etc.). In the example of FIG. 6, step 120 helpsreduce any overshoot that occurs after time T₅.

The value of the new T_(A) set at step 120 may be determined in multiplemanners. In some embodiments, the value is set to be less than thepatient target temperature 88 by a fraction of the overshoot valueT_(over) (FIG. 6). The fraction may be one-half in some embodiments,although other fractions may be used. In still other embodiments, T_(A)may be defined in another manner.

In the illustrative graph shown in FIG. 6, controller 66 has notimplemented step 120. However, the following description of step 120will utilize the graph of FIG. 6 to more fully explain the overshootreduction accomplished via step 120. After calculating a new T_(A) atstep 120, controller 66 returns to steps 102, 104, and 106, where itmonitors the patient temperature and the fluid temperature (step 102),controls the fluid temperature using control loops 74 a and 74 b (step104), and compares the patient temperature to the new T_(A) value(calculated in step 120). Thus, controller 66 implements the loop ofsteps 102, 104, and 106 until the patient's temperature reaches the newT_(A) value. Although controller 66 has not utilized step 120 in FIG. 6(as noted above), FIG. 6 includes a time labeled T₄, and T₄ correspondsto one potential time at which the patient's temperature would equal thenew T_(A) value were controller 66 implementing step 120.

At time T4, controller 66 would move onto step 108 and stop the flow offluid, and thereafter follow steps 110-118 in the manner previouslydescribed. These steps would help reduce the second overshoot of thepatient's temperature past target temperature 88. It can be seen fromFIG. 6, however, that step 120 was not actually performed in the exampleillustrated therein because, when the patient reaches the targettemperature 88 for the second time at T₅, the fluid temperature 76 iswell above the target temperature 88. Consequently, the continueddelivery of fluid at this elevated temperature to the thermal pads 24would likely cause the patient's temperature to rise above (overshoot)the target temperature 88 in the time period subsequent to time T₅. Hadstep 120 been performed in the example of FIG. 6, controller 66 wouldhave begun reducing the temperature of the fluid at a point earlier thanshown in FIG. 6 so that, at point T₅, the temperature of the fluid 76was significantly closer to the target temperature 88.

Returning to step 112 of algorithm 98 (FIG. 5), controller 66 proceedsto step 122 (and does not shut off bypass valve 56) if it detects thatthe rate of change of the patient's temperature has started to shallowout by more than the threshold used in step 112. FIG. 7 illustrates anexample of this situation. Time T₆ of FIG. 7 corresponds to step 108 inalgorithm 98. That is, controller 66 has determined at time T₆ of FIG. 7that the patient's temperature has reached temperature T_(A). Controller66 therefore shuts off bypass valve 56 at time T₆ and begins monitoringthe reaction of the patient's temperature to this shut off. Thismonitoring takes place from time T₆ to T₇ and is performed in step 110.As can be seen in FIG. 7, in the moments after T₆ (and before T₇), therate at which the patient's temperature 90 is dropping changessignificantly from the rate at which the patient's temperature 90dropped in the moments before T₆. Controller 66 therefore determinesthat the patient is unlikely to reach the target temperature 88 withoutsupplying additional cold fluid to thermal pads 24. In other words,controller 66 determines at step 112 that the patient's rate oftemperature change has shallowed out more than a threshold, andtherefore proceeds to step 122.

At step 122, controller 66 opens up bypass valve 56, restarting thesupply of cold fluid to thermal pads 24. Controller 66 also restarts (tothe extent it had stopped doing so at time T₆) the temperature controlof the circulating fluid using control loops 74 a and 74 b. In theexample shown in FIG. 7, controller 66 starts warming the fluid insidethermal control unit 22 in the time period between T₆ and T₇, andcontroller 66 terminates this warming at time T₇ (and starts usingcontrol loops 74 a and 74 b again). In other embodiments, controller 66may simply shut off heat exchanger 40 in the interim between T₆ and T₇.

After opening bypass valve 56 at step 122, controller 66 proceeds tostep 124 where it calculates a new T_(A) value. The new T_(A) value ofstep 124 is not the same as the new TA value calculated in step 120,although it may be calculated in a number of different manners. In oneembodiment, the new T_(A) value of step 124 is set equal to a valuehalfway between the patient target temperature 88 and the old T_(A)value (e.g. T_(A)new=((T_(A)old−Pat. Targ. Temp)/2)+Pat. Targ. Temp.)Variations of this formula, or still other manners of calculating thenew T_(A) value at step 124, may be used. After calculating the newT_(A) value, controller 66 proceeds back to step 102 where itrecommences reading the fluid and patient temperatures. After readingthe fluid and patient temperatures at step 102, the fluid and patienttemperature values are used in the control loops 74 a and 74 b at step104. Control then moves to step 106 where controller 66 determineswhether the patient's temperature has reached the new T_(A) value thatwas calculated at step 124. Steps 102, 104, and 106 continue until thepatient's temperature reaches the new T_(A) value. This point is labeledT₈ in FIG. 7 and corresponds to step 108.

At step 108, controller 66 shuts off bypass valve 56 again and proceedsto repeat steps 110 and 112 in the same manner previously described.With respect to FIG. 7, controller 66 closes the bypass valve at T₈,monitors the temperature variables at step 110 until time T₉, and thenproceeds to step 112. In the example of FIG. 7, controller 66 determinesat step 112 (time T₉) that the rate of change of the patient'stemperature between times T₈ and T₉ has not bottomed out so much thatthe patient will not likely reach target temperature 88 without furtherfluid delivery to thermal pads 24. In other words, at time T₉,controller 66 moves to step 114 and shuts off bypass valve 56.Controller 66 leaves bypass valve 56 shut off until time T₁₀, at whichpoint the fluid has warmed sufficiently to help prevent overshoot of thepatient's temperature. Accordingly, at time T₁₀ (step 118) controller 66opens bypass valve 56 again and begins delivering fluid to thermal pads24.

In the example illustrated in FIG. 6, algorithm 98 reaches step 112 onceand proceeds to step 114. In the example illustrated in FIG. 7,algorithm 98 reaches step 112 twice and the first time controller 66proceeds to step 122 and second time controller 66 proceeds to step 114.It will be understood, of course, that FIGS. 6 and 7 illustrate only twopotential usage scenarios of algorithm 98, and that many othervariations are possible. For example, there is no limit to the number oftimes controller 66 might proceed to step 122 before eventuallyproceeding to step 114. As another example, neither FIG. 6 nor FIG. 7illustrates a situation where step 120 is followed. In those situationswhere controller 66 executes step 120, controller 66 may subsequentlybranch to step 122 at step 112 or it may branch to step 114 at step 112.After moving through steps 114, 116, and 118 a second time, controller66 may be programmed to proceed to step 120 yet another time.

Although algorithm 98 has been described herein as stopping the flow offluid to thermal pads 24 at step 108, it will be understood that variousmodifications can be made to this. In one modified embodiment,controller 66 deactivates heat exchanger 40 but continues to supplyfluid to thermal pads 24 at step 108 and reactivates heat exchanger 40at steps 116 and/or 122 (and continues to supply fluid to thermal pads24). The remainder of algorithm 98 remains the same in this modifiedembodiment. In other modified embodiments, controller 66 reduces theflow of fluid to thermal pads 24 at step 108, but does not completelystop the flow of fluid. Full fluid delivery to pads 24 returns at steps116 and/or 122. In still other modified embodiments, controller 66combines the reduction of fluid flow at step 108 with the deactivationof heat exchanger 40, and the resumption of full fluid flow at steps 116and 122 with the reactivation of heat exchanger 40. Still othervariations are possible.

It will be understood that, although FIGS. 6 and 7 illustrate algorithm98 being applied to a situation where the patient's target temperature88 is set below the patient's initial temperature (i.e. the patient isbeing cooled by thermal control system 20), algorithm 98 is equallyapplicable to situations in which the patient is being warmed. Indeed,algorithm 98 is agnostic as to relationship of the patient's initialtemperature to the target temperature 88. The same steps andcalculations as discussed above with respect to FIGS. 5-7 are usedregardless of whether thermal control system 20 is being used to cool orwarm a patient.

FIG. 8 illustrates a second temperature control algorithm 130 that maybe followed by controller 66 of thermal control unit 22. Controlalgorithm 130 begins at step 132 where a user sets a desired patienttarget temperature 88. Step 132 is the same as step 100 of algorithm 98.After step 132, controller 66 proceeds to step 134 where it takesreadings of the patient's temperature, the fluid temperature insidethermal control unit 22, and determines the slope and/or othercharacteristics of past values of these temperatures. Step 134 is alsothe same as step 102 of algorithm 98.

After step 134, controller 66 moves to step 136 where it uses the latestreadings of the patient's temperature 90 and the fluid temperature 76 inthe control loops 74 a and 74 b. Controller 66 then sends aheating/cooling command to heat exchanger 40 based on the output ofthese control loops. Step 136 is the same as step 104 of algorithm 98.

After step 136, controller 66 moves to step 138 where it determineswhether or not the patient has yet reached the target temperature 88. Ifthe patient has not yet reached target temperature 88, control returnsto steps 134 and 136 and controller 66 continues to send heating andcooling commands to heat exchanger 40 using the closed control loops 74a and 74 b and the current readings of patient and fluid temperaturetaken during steps 134.

When the patient's temperature 90 eventually reaches the targettemperature, controller 66 moves from step 138 to step 140. At step 140,controller 66 determines whether the current temperature of the fluid 76will cause or exacerbate overshoot of the target temperature 88 if thefluid is delivered to thermal pads 24. This is determined by examiningthe current fluid temperature 76 and determining whether the patient'sarrival at the target temperature occurred through cooling or throughheating. If the patient arrived at the target temperature 88 by cooling,controller 66 determines at step 140 if the current temperature of thefluid is less than target temperature 88. If it is, controller 66concludes that continuing to deliver fluid to thermal pads 24 at atemperature below target temperature 88 to a patient who was just cooledto target temperature 88 will likely cause or exacerbate overshoot, andcontroller 66 therefore moves to step 142 where it shuts off bypassvalve 56. If it is not, controller 66 concludes that continuing todeliver fluid to thermal pads 24 at a temperature warmer than the targettemperature will likely not cause or exacerbate overshoot, and thereforemoves back to step 134 while keeping bypass valve 56 open.

Conversely, if the patient arrived at target temperature 88 by warming,controller 66 determines at step 140 if the current temperature of thefluid is more than target temperature 88. If it is, controller 66concludes that continuing to deliver fluid to thermal pads 24 at atemperature above target temperature 88 to a patient who was just warmedto target temperature 88 will likely cause or exacerbate overshoot, andcontroller 66 therefore moves to step 142 where it shuts off bypassvalve 56. If it is not, controller 66 concludes that continuing todeliver fluid to thermal pads 24 at a temperature below targettemperature 88 will not likely cause or exacerbate overshoot, andtherefore moves back to step 134 while keeping bypass valve 56 open.

The determinations made by controller 66 at step 140 may be betterunderstood with respect to the example shown in FIG. 6. Although FIG. 6illustrates an example of patient and fluid temperatures when thermalcontrol unit 22 is following algorithm 98, the graphs of temperatureshown therein can be used to explain when and how controller 66 makesits decision at step 140. The results of those decisions, however, arenot shown in FIG. 6 because, as noted, FIG. 6 illustrates an exemplaryresult of control algorithm 98, not control algorithm 130.

The decision of step 140 of algorithm 130 is first made when thepatient's temperature reaches the target temperature 88 for the firsttime, which in the graph of FIG. 6 occurs at time T₁₁. Further, in thegraph of FIG. 6, the patient arrives at target temperature 88 at timeT₁₁ after being cooled. Accordingly, at time T₁₁, controller 66—whenfollowing algorithm 130—looks at the temperature of the fluid 76 at timeT₁₁. In FIG. 6, this fluid temperature 76 is above target temperature88. Consequently, if controller 66 continues to deliver this fluid tothermal pads 24, it is not going to cause or exacerbate overshoot.Instead, it will resist overshoot. This is because any overshoot thatoccurs at time T₁₁ will be an overshoot where the patient's temperaturemoves below target temperature 88. As a result, by delivering fluid tothermal pads 24 that is warmer than target temperature 88, the patient'sovershoot will be reduced (or eliminated). Had the fluid temperature 76in FIG. 6 been below target temperature 88 at time T₁₁, controller 66would have concluded that continued delivery of the fluid to thermalpads 24 at time T₁₁ would exacerbate the overshoot, and therefore wouldhave moved to step 142 of algorithm 130 and shut off bypass valve 56.

FIG. 6 also illustrates the patient's temperature arriving at targettemperature 88 a second time. This occurs at time T₅. When controller 66is following algorithm 130 and the patient arrives at the targettemperature 88 for the second time (or any times thereafter), controller66 once again goes through the above-described analysis at step 140. Inthe example shown in FIG. 6, controller 66 would proceed to step 142 andshut off bypass valve 56 at time T₅. This is because the patient arrivedat target temperature 88 at time T₅ by being warmed and the temperatureof the fluid 76 at time T₅ is above target temperature 88. Accordingly,if thermal control unit 22 were to continue to deliver fluid to thermalpads 24 at time T₅ (and thereafter), the fluid would continue to warmthe patient, which would lead to greater overshoot. Accordingly, in theexample shown in FIG. 6, controller 66 would move to step 142 ofalgorithm 130 and shut off bypass valve 56.

After controller 66 has moved to step 142, it follows steps 144 and 146to determine when to open up bypass valve 56. At step 144, controller 66continues to heat or cool the circulating fluid in accordance with thecommands generated from control loops 74 a and 74 b. At step 146,controller 66 performs the same analysis it did at step 140. That is, itlooks at the current patient temperature and the current fluidtemperature and determines whether or not the delivery of fluid at itscurrent temperature to thermal pads 24 would cause or exacerbateovershoot. If it would, control returns back to step 144 where furthertemperature adjustments are made. After the further temperatureadjustments are made, controller 66 moves again to step 146 to determineif overshoot will occur or be exacerbated by delivering the fluid to thethermal pads. This back and forth between steps 144 and 146 keeps ongoing until the fluid eventually reaches a temperature where it will notcause or exacerbate any overshoot in the patient's temperature. At thatpoint, controller 66 moves to step 148 where it opens bypass valve 56,allowing fluid to flow again to thermal pads 24. After step 148,controller 66 returns to step 134.

During the performance of steps 144 and 146, which may continue for aslong as necessary for thermal control unit 22 to adjust the fluidtemperature to a point where its delivery to thermal pads 24 will notcause or exacerbate overshoot, bypass valve 56 remains closed. As aresult, the heating or cooling of the fluid that occurs during thesesteps is confined to thermal control unit 22. Pump 34 remains activeduring this time, but the circulation caused by pump 34 is restricted tooccurring only internally because all of the fluid travels throughbypass line 52 rather than exiting out outlet manifold 42.

In the example of algorithm 130 described above, the determination ofwhether or not fluid delivery to thermal pads will contribute toovershoot is based on examining the current fluid temperature'srelationship to the target temperature 88. It will be understood thatthis examination may be modified. In some embodiments, for example,controller 66 examines the current fluid temperature's relationship to adifferent value, such as range of temperatures (which may be definedwith respect to the target temperature). In some such embodiments,whether or not the current fluid temperature 76 falls within that rangeor not is the sole criteria for determining whether to open or closebypass valve 56 at steps 142 and 148. In other of such embodiments,whether or not the current fluid temperature 76 falls within that rangeor not is used in conjunction with other factors to determine whether toopen or close bypass valve 56. The other factors include, but are notlimited to, the determination of whether the patient's temperature 90arrived at target temperature 88 via heating or cooling, as noted above.

FIG. 9 illustrates an alternative embodiment of a thermal control unit22′. Those elements of thermal control unit 22′ that are the same asthermal control unit 22 are labeled with the same reference number and,unless explicitly mentioned otherwise below, operate in the same manneras described with respect to thermal control unit 22. Those elements ofthermal control unit 22′ that are new are provided with a new referencenumber, and those elements of thermal control unit 22′ that are similarbut modified from thermal control unit 22 are provided with the samereference number followed by a prime (′) symbol.

Thermal control unit 22′ of FIG. 9 differs from thermal control unit 22in that thermal control unit 22′ is adapted to selectively move fluidreservoir 32′ into and out of line with circulation channel 36. Thermalcontrol unit 22′ accomplishes this through the inclusion of reservoirvalve 150. Reservoir valve 150 is shown positioned in FIG. 9 incirculation channel 36 between air remover 58 and valve 60, although itwill be understood that reservoir valve 150 may be moved to differentlocations within circulation channel 36. Reservoir valve 150 is coupledto circulation channel 36 as well as a reservoir channel 152.

When reservoir valve 150 is open, fluid from air remover 58 flows alongcirculation channel 36 to pump 34 without passing through reservoir 32′and without any fluid flowing along reservoir channel 152. Whenreservoir valve 150 is closed, fluid from air remover 58 flows alongreservoir channel 152, which feeds the fluid into reservoir 32′. Fluidinside of reservoir 32′ then flows back into circulation channel 36 viavalve 60. Once back in circulation channel 36, the fluid flows to pump34 and is pumped to the rest of circulation channel 36 and thermal pads24 and/or bypass line 52. In some embodiments, reservoir valve 150 iscontrollable to be either fully open or fully closed, while in otherembodiments, reservoir valve 150 is controllable to be partially open orpartially closed. In either case, reservoir valve 150 is under thecontrol of controller 66. Controller 66 opens and closes reservoir valve150 in some embodiments when disinfectant is mixed into the circulatingfluid in order to disinfect reservoir 32′ and circulation channel 36.Controller 66 also closes and opens reservoir valve 150 for otherpurposes which are discussed in greater detail below.

Thermal control unit 22′ also includes a reservoir temperature sensor154. Reservoir temperature sensor 154 reports its temperature readingsto controller 66. When reservoir valve 150 is open, the fluid inside ofreservoir 32′ stays inside of reservoir 32′ (after the initial drainageof the amount of fluid needed to fill circulation channel 36 and thermalpads 24). This residual fluid is not affected by the temperature changesmade to the fluid within circulation channel 36 as long as reservoirvalve 150 remains open. This is because the residual fluid that remainsinside of reservoir 32′ after circulation channel 36 and thermal pads 24have been filled does not pass through heat exchanger 40 and remainssubstantially thermally isolated from the circulating fluid. Two resultsflow from this: first, heat exchanger 40 does not need to expend energyon changing the temperature of the residual fluid in reservoir 32′, andsecond, the temperature of the circulating fluid in circulation channel36 will deviate from the temperature of the residual fluid as thecirculating fluid circulates through heat exchanger 40.

Temperature control algorithm 160 of FIG. 10 utilizes the divergencebetween the temperature of the residual fluid in reservoir 32′ and thetemperature of the circulating fluid when it is advantageous to do so.That is, controller 66 monitors the temperature of the residual fluid inreservoir 32′ and if it warmer than the circulating fluid in circulationchannel 36, controller 66 may selectively close valve 150 and mix someor all of the residual fluid into circulation channel 36 if controller66 needs to quickly warm the temperature of the circulating fluid.Similarly, if the temperature of the residual fluid is colder than thetemperature of the circulating fluid, controller 66 may selective closevalve 150 and mix some or all of the residual fluid into circulationchannel 36 if controller 66 needs to quickly cool the temperature of thecirculating fluid. The details of control algorithm 160 will now bedescribed with respect to FIG. 10.

Control algorithm 160 starts at step 162 where the user selects a targettemperature 88 for the patient. From step 162, controller 66 moves tostep 164 where it takes fluid temperature and patient temperaturereadings. The readings are used by controller 66 during step 166 todetermine what heating or cooling command to issue to heat exchanger 40.The command to issue to heat exchanger 40 is determined at step 166using control loops 74 a and 74 b. After sending out one or more heatingor cooling commands at step 166, controller 66 moves to step 168 whereit determines whether or not the addition of the residual fluid insidereservoir 32′ would be helpful in achieving a target temperature for thecirculating fluid. This determination is made using a current reading ofthe temperature of the residual fluid inside reservoir 32′ (as measuredby sensor 154), a current reading of the circulating fluid insidethermal control unit 22′ (as measured by outlet temp sensor 44), and thepatient target temperature 88.

In general, controller 66 does not initially utilize any of the residualfluid inside reservoir 32′ until after the patient has reached targettemperature 88 the first time (e.g. time T₁₁ in FIG. 6 or shortly aftertime T₁₀ in FIG. 7). This is because when thermal control unit 22′ isinitially used, the residual fluid tends to remain at room temperaturewhile the circulating fluid is controlled via heat exchanger 40 toward atemperature that will either heat or cool the patient to the targettemperature. During that initial heating or cooling of the patient, theresidual fluid at room temperature will not be helpful. However, oncethe patient has reached the target temperature 88 (or once the patienthas come close to the target temperature 88, such as, but not limitedto, temperature T_(A) discussed above with respect to algorithm 98),controller 66 generally needs to switch from heating the circulatingfluid to cooling the circulating fluid, or vice versa. It is at thesechanges in thermal direction that the residual fluid inside of reservoir32′ can be most helpful for rapidly changing the temperature of thecirculating fluid. It will be understood, however, that controller 66may utilize the residual fluid inside of reservoir 32′ at other times,including before the patient reaches the target temperature.

Controller determines whether the residual fluid is helpful or not atthese moments by determining if the temperature of the residual fluid iscloser to the fluid target temperature 78 than the current temperatureof the circulating fluid. If it is, controller 66 moves to step 170 andcloses reservoir valve 150 such that the reservoir 32′ becomes part ofcirculation channel 36. That is, instead of diverting the circulatingfluid around reservoir 32′ (which occurs when valve 150 is open), theclosing of valve 150 diverts the circulating fluid through reservoir32′. The residual fluid is thus mixed with the circulating fluid and thetemperature of the circulating fluid is quickly adjusted upward ordownward, depending upon the difference in temperature between thecirculating fluid and the residual fluid.

In some embodiments, controller 66 keeps valve 150 closed for as long asit takes to ensure that all, or substantially all, of the residual fluidinside reservoir 32′ has passed out of reservoir 32′ and mixed into thefluid inside of circulating channel 36. In order to measure this amountof time, thermal control unit 22′ may include a depth or volume sensorto measure how much residual fluid is in reservoir 32′, as well as oneor more flow sensors that measure how much fluid has been delivered tofluid reservoir 32′ from reservoir channel 152. In other embodiments,controller 66 may continue to close valve 150 for a time period that isbased on the temperature readings from temperature sensors 44 and 154.In some of these embodiments, controller 66 may continue to close valve150 until the temperature readings from reservoir temp sensor 154 andoutlet temp sensor 44 come within a predetermined range of each other.In still other embodiments, other criteria may be used for determininghow long to keep reservoir valve 150 closed. Regardless of the criteriaused, controller 66 passes back to step 164 after opening reservoirvalve 150.

Algorithm 160 may be more easily understood with respect to an example,such as the example of FIG. 6. As noted previously, FIG. 6 illustratesthe results of one example of algorithm 98; however, the graphs shown inFIG. 6 can be used to illustrate how controller 66 would react to thetemperatures shown in FIG. 6. As shown therein, the fluid both insidereservoir 32′ and in circulation channel 36 initially starts (time T₀)at a temperature that, in most situations will be room temperature(R_(T)). In the example shown in FIG. 6, controller 66 starts to coolthe fluid in circulation channel 36 after the thermal therapy starts andcontinues to cool the fluid until time T₁. From the initiation of thethermal therapy until time T₁, the fluid in reservoir 32′ will notassist in the thermal treatment of the patient. This is because theresidual fluid in reservoir 32′ remains substantially at roomtemperature from time T₀ until time T₁, and the mixing of this residualfluid with the circulating fluid would only cause the circulating fluidto warm up, which is undesired during the time period from T₀ to T₁.

When time T₁ is reached in the example of FIG. 6, controller 66, whenfollowing algorithm 160, may determine that mixing the residual fluidwith the circulating fluid would assist in the thermal therapy of thepatient. This is because at time T₁ controller 66 begins warming thecirculating fluid and the residual fluid is at a warmer temperature(room temperature) than the circulating fluid. Thus, the mixing of theresidual fluid would cause a faster increase in the temperature of thecirculating fluid. Controller 66 may therefore determine that such afaster increase in the temperature of the circulating fluid isdesirable. This determination may be based on other factors as well, aswill be discussed more below. At any point between T₁ and T₁₂,controller 66 may mix the residual fluid with the circulating fluid.However, after time T₁₂, controller 66 will not mix the residual fluidwith the circulating fluid because the residual fluid will be colderthan the circulating fluid and controller 66 is attempting to heat thefluid at that time.

After time T₁₂, controller 66 will not mix the residual fluid with thecirculating fluid for at least as long as it takes for controller 66 toheat the circulating fluid to the desired temperature 78. Once at thedesired temperature, controller 66 will again consider mixing theresidual fluid with the circulating fluid at step 168 if controller 66determines that the temperature of the fluid needs to be decreased. Thisis because the temperature of the residual fluid will be lower than thetemperature of the circulating fluid after it has reached its maximum,and releasing the residual fluid at any time before the circulatingfluid needs to be cooled would only add to the work of heat exchanger 40and delay the arrival of the fluid at target temperature 78.

The potential times at which mixing residual fluid with circulatingfluid are therefore limited to times when the residual fluid is closerto the target fluid temperature 78 than the current temperature 76 ofthe circulating fluid. During those times, controller 66 may close valve150, or it may decide not to close valve 150. In making thisdetermination, controller 66 examines, in at least some embodiments, therate at which the temperature of the circulating fluid 76 is changing,the amount of error that has accumulated in the integral term of thecontrol loop 74 a, and/or other factors. Controller 66 may also utilizeother factors in making this determination.

Controller 66 may also, or alternatively, control reservoir valve 150 inorder to help avoid or reduce overshoot. For example, in the exemplarygraph of FIG. 6, at the time the patient's temperature reaches targettemperature 88 the second time (T₅), the temperature of the circulatingfluid 76 is above the patient target temperature. It may therefore bedesirable to quickly adjust the temperature of the circulating fluiddownward so that the patient's temperature does rise above targettemperature 88 (overshoot it). At time T₅ (or in the moments before),controller 66 may therefore mix the residual fluid with the circulatingfluid in order to more quickly drop the temperature of the circulatingfluid.

The selective shifting of reservoir 32′ into and out of circulationchannel 36 may be carried out in one of two ways, depending upon theparticular embodiment of thermal control unit 22′ being implemented. Inthe embodiment of thermal control unit 22′ described above, thermalcontrol unit 22′ does not actively change the temperature of theresidual fluid inside of reservoir 32′. In an alternative embodiment,which will now be described, thermal control unit 22′ includes a heatexchanger 156 positioned inside reservoir 32′ (or in a location closeenough to thermal reservoir 32′ to allow heat to be exchanged betweenthe residual fluid inside reservoir 32′ and heat exchanger 156. Heatexchanger 156 is under the control of controller 66 and includes aheater adapted to heat the temperature of the residual fluid at certaintimes. More specifically, controller 66 controls the heater of heatexchanger 156 such that the residual fluid inside reservoir 32′ isheated when a patient's temperature is being cooled. This enablescontroller 66 to abruptly increase the temperature of the circulatingfluid at a desired moment-such as at or near the time the patientarrives at the patient target temperature—by closing reservoir valve 150and allowing the heated residual fluid inside reservoir 32′ to mix withthe circulating fluid.

In some embodiments, heat exchanger 156 also includes a chiller adaptedto chill the temperature of the residual fluid inside of reservoir 32′.In such embodiments, controller 66 controls the chiller of heatexchanger 156 such that the residual fluid inside reservoir 32′ iscooled when a patient's temperature is being warmed. This enablescontroller 66 to abruptly decrease the temperature of the circulatingfluid at a desired moment—such as at or near the time when the patientarrives at the patient target temperature—by closing reservoir valve 150and allowing the chilled residual fluid inside reservoir 32′ to mix withthe circulating fluid.

The heating and/or cooling of fluid inside reservoir 32′ helpscontroller 66 abruptly change the temperature of the circulating fluid,which is particularly useful in situations where the patient is arrivingat, or near to arriving at, the patient target temperature. By abruptlychanging the temperature of the circulating fluid at these moments,controller 66 can help to reduce or avoid temperature overshoot. This isbecause, without the addition of the residual fluid to the circulatingfluid at these times, it would likely otherwise take additional time tochange the temperature of the fluid to the desired fluid temperature,and during that transition period, the temperature of the patient maycontinue to move beyond the target patient temperature.

It will be understood that, although FIG. 9 illustrates thermal controlunit 22′ with heat exchanger 156, heat exchanger 156 may be omitted insome embodiments of thermal control unit 22. Further, when heatexchanger 156 is included, it may be implemented solely as a chiller,solely as a heater, or as a combination of both a heater and a chiller.Still further heat exchanger 156—whether implemented as a heater, achiller, or both—may be added to any of the other embodiments of thethermal control units described herein.

The physical form of heat exchanger 156 may take on a variety ofdifferent forms. In some embodiments, heat exchanger 156 is built intoremovable reservoir 32′ and includes electrical contacts that come intoelectrical communication with contacts contained within thermal controlunit 22′ when reservoir 32′ is inserted into thermal control unit 22′.The electrical contacts allow controller 66 to control and/or power heatexchanger 156. In other embodiments, heat exchanger is inserted intoreservoir 32′, but is removable therefrom (as well as from thermalcontrol unit 22′). In still other embodiments, heat exchanger 156 isattached to a movable arm that a user moves out of the way when addingor removing reservoir 32′ to or from thermal control unit 22′. Whenreservoir 32′ is seated within thermal control unit 22′, the arm ismoved such that heat exchanger 156 is positioned in physical contactwith the fluid within reservoir 32′. In still other embodiments, heatexchanger 156 is built into thermal control unit 22′ in a stationarymanner and exchanges heat with the residual fluid by having the heatpass through one or more of the walls of reservoir 32′.

FIG. 11 illustrates another example of a temperature control algorithm172 that may be utilized by controller 66 of thermal control unit 22′.Algorithm 172 illustrates one manner in which algorithms 130 and 160 maybe combined together. Other manners are, of course, possible. In themanner illustrated in FIG. 11, steps 132′, 134′, 136′, 138′, 140′, 142′,144′, 146′, and 148′ are the same as steps 132, 134, 136, 138, 140, 142,144, 146, and 148, respectively, of algorithm 130 of FIG. 8. Similarly,steps 168′ and 170′ are the same as steps 168 and 170 of the algorithm160 of FIG. 10. Step 168′ is reached after controller 66 performs step142′ and shuts the bypass valve 56, thereby shutting off further flow tothe thermal pads 24. After shutting off bypass valve 56, controller 66determines if the residual fluid in the reservoir 32′ (which may beactively heated, actively cooled, or left alone) will reduce anyovershoot or not. If the answer is no, controller 66 returns to steps144′ and continues to operate in the manner previously described forstep 144 of algorithm 130. If controller 66 determines that the residualfluid in the reservoir 32′ will help to reduce or eliminate anyovershoot, controller 66 proceeds to step 170′ and mixes the residualfluid with the circulating fluid. This is done by closing reservoirvalve 150. Reservoir valve 150 remains closed for any of the timeperiods discussed above. After step 170′, controller 66 returns to step144′ and proceeds in the same manner discussed above with respect tostep 144 and algorithm 130.

Algorithm 172 adds to algorithm 130 by having controller 66 assesswhether the mixing of the residual reservoir fluid with the circulatingfluid will expedite moving the temperature of the circulating fluid morequickly to its target temperature. As noted previously, algorithm 130 isdesigned to stop delivering fluid to thermal pads 24 if the temperatureof the circulating fluid is such that further delivery of that fluid tothe thermal pads 24 will exacerbate the patient's overshoot. Whencutting off fluid delivery to thermal pads 24, algorithm 130 warms orcools the circulating fluid until it reaches a temperature that will nolonger exacerbate temperature overshoot, at which point fluid deliveryto thermal pads 24 resumes. Algorithm 172 expedites the internal heatingor cooling of the fluid by, when appropriate, mixing the residual fluidwith the circulating fluid in order to change the temperature of thecirculating fluid more quickly, thereby reducing the time during whichfluid is not delivered to thermal pads 24.

FIG. 12 illustrates an example of a graph 174 of a patient'stemperature, fluid temperature, and a target patient temperature whencontroller 66 of either thermal control unit 22 or 22′ is operatingaccording to yet another temperature control algorithm. In thetemperature control algorithm of FIG. 12, controller 66 uses controlloops 74 a and 74 b (or modifications thereto) to control thetemperature of the circulating fluid and the automatically adjust thetemperature of a patient toward target temperature 88. The algorithm ofFIG. 12 differs from the previously described algorithms in thatcontroller 66 utilizes different coefficients in the control loops 74 aand 74 b at different points during the thermal treatment. The use ofdifferent coefficients at different time periods helps to achieve thepatient's target temperature more quickly, yet with a reduced (orabsent) amount of overshoot.

As with the other algorithms described herein, the patient's temperaturebegins at an initial temperature P_(I). After thermal therapy starts,the temperature of the fluid circulating to the thermal pads 24 isreduced, and the patient's temperature 90 is adjusted toward patienttarget temperature 88. When the patient's temperature first falls withina range 176 of the target temperature 88, signified by point B in FIG.12, controller 66 switches to using a different set of coefficients forat least one of control loops 74 a and 74 b. In some embodiments,controller 66 performs the switchover at point B to a different set ofcoefficients only if one or more criteria are met at or near the time ofpoint B. For example, in some embodiments, controller 66 analyzes theaccumulated error in the integral term of either or both of controlloops 74 a and 74 b and switches to a different set of coefficients ifthe integral error has accumulated to a value greater than a threshold.If the integral error has not accumulated to more than the threshold,controller 66 continues to use the same set of coefficients. In otherembodiments, other thresholds may be used for one or more differentcriteria.

The time (point B in FIG. 12) at which the coefficient transition, ifany, occurs may be based on several variables. In some embodiments,point B may be selected using the same criteria as point T_(A) discussedabove with respect to algorithm 98. In some embodiments, point B may bechosen as a patient temperature that corresponds to a predefinedfraction of the difference between the patient's initial temperature(P_(I)) and the target temperature. In still other embodiments, point Bmay be chosen based on the slope of the patient's temperature and aprediction of when the patient's temperature will arrive at the targettemperature 88. In these latter embodiments, point B may be selected asa predefined amount of time before the patient target temperature 88 ispredicted to be achieved, given the recent slope of the patient'stemperature changes. Still other criteria may be used.

After switching to a different set of coefficients at point B,controller 66 continues to use the newly selected coefficients untilafter the patient's temperature has reached target temperature 88. Afterreaching target temperature 88, controller 66 re-assesses thecoefficients at point D in FIG. 12. Point D refers to a time at whichthe patient's temperature has returned, after exiting, to within thedefined range 176 of the target temperature 88. At point D, controller66 once again re-assesses the current slope of the patient'stemperature, the current error in the patient's temperature (differencebetween target temperature 88 and the patient's current temperature),and potentially other variables (e.g. the accumulated error in theintegral terms of loops 74 a and/or 74 b). Controller 66 then decideswhether to switch to using different coefficients or not. When switchingto different coefficients, the different coefficients may be the same asthose previously used prior to point B, or they may be coefficients thatare completely new, or a blend of the two. In some embodiments, thecoefficients are selected based on the current error value in thepatient's temperature. For example, the derivative coefficient (if aderivative term is used) may be based on the current value of thederivative term, the proportional coefficient (if a proportional term isused) may be based on the current error value in the patient'stemperature, and the integral coefficient (if an integral term is used)may be based on the current value of the integral term. Other factorsmay also be used to select and/or calculate one or more newcoefficients.

Although not illustrated in FIG. 12, one or more assessment points afterpoint D may exist where controller 66 again assesses whether or not tochange the coefficients used in control loops 74 a and/or 74 b. Thesemay occur each time the patient's temperature overshoots the targettemperature, or at other times. As with all of the changes to thecoefficients, any new coefficients are selected in order to reduceovershoot and/or the magnitude of oscillations about the targettemperature 88.

In some embodiments, the new coefficients that are used are chosen basedupon the rate at which the patient's temperature is approaching thepatient target temperature 88. If, for example, the rate of change ofthe patient's temperature is steep in the vicinity of the targettemperature 88 such that it is likely that the patient's temperaturewill overshoot the target temperature 88 a relatively large amount (aspredicted at an assessment point, such as points B or D), controller 66selects a new gain coefficient that has a smaller value. On the otherhand, if the rate of change of the patient's temperature is too shallowwhen in the vicinity of the target temperature 88 such that it is likelythat the patient's target temperature will not be reached in arelatively short time, controller 66 selects a new gain coefficient thathas a larger value.

It will be understood that, in some embodiments, the number ofassessment points reached by controller 66 will vary in response to thereaction of the patient undergoing thermal treatment. Thus, for example,in those embodiments where range 176 is defined as a predefined rangearound the patient target temperature 88, controller 66 may only reachan assessment point (point B in FIG. 12) once. This is particularly truewhere, after reaching the first assessment point, the patient'stemperature remains within a tighter range of the target temperature 88than range 176. In other words, if the patient's temperature neverventures outside of range 176 after point B, then point D (and anyfuture assessment points) may never occur for that particular thermaltreatment session. Therefore, the number of times controller 66 switchescoefficients may vary in response to the particular patient undergoingthermal treatment and his or her reaction to the thermal treatment.

It will be understood that, although the algorithm illustrated in FIG.12 has been described herein as a separate algorithm, it may be mixedwith any of the algorithms 98, 130, 160, and/or 172 previouslydescribed. Alternatively, of course, the algorithm of FIG. 12 may beused separately and without any of algorithms 98, 130, 160, and 172. Itwill also be understood that the algorithm of FIG. 12 may be used withboth thermal control unit 22 and thermal control unit 22′, as well asother types of thermal control units. It will also be understood that,although algorithms 98 and 130 have been described herein as being usedwith thermal control unit 22, either or both of these algorithms may beused with thermal control unit 22′ as well. Still further, any of thetemperature control algorithms disclosed herein may be usedindividually, or combined with any one or more of the other algorithmsdisclosed herein.

Various modifications may also or alternatively be made to the physicalconstruction of thermal control units 22 and/or 22′ beyond thosedescribed above. For example, the particular order of the componentsalong circulation channel 36 of control units 22, 22′ may also oralternatively be varied from what is shown in the drawings. For example,although the drawings depict pump 34 as being upstream of heat exchanger40, and air remover 58 as being upstream of pump 34, this order may bechanged. Air remover 58, pump 34, heat exchanger 40 and reservoir 32 (or32′) may be positioned at any suitable location along circulationchannel 36.

Bypass valve 56 may also be implemented as a conventional check valvethat automatically opens to allow fluid to flow through bypass line 52when the pressure in circulation channel 36 exceeds a particularpressure. In order to control the flow of fluid through bypass line 52,an additional valve may be positioned between bypass valve 56 and outletmanifold 42 that is controllable by controller 66. When controller 66shuts this additional valve, the fluid pressure within circulationchannel 36 adjacent bypass valve 56 builds up until valve 56 opens andfluid is allowed to flow through bypass line 52. Still other manners ofcontrolling the flow of fluid through bypass line 52 may also beimplemented.

When carrying out any of the aforementioned temperature controlalgorithms 98, 130, 160, and/or 172, controller 66 may also beconfigured to make one or more adjustments to condenser 47 (if included;see FIG. 3 and FIG. 9) within thermal control unit 22 or 22′, and/or fan51 that blows heat away from the condenser 47 (in an air cooledcondenser), and/or a speed of compressor 45. In a liquid cooledcondenser, fan 51 may be replaced by an impeller that pumps liquid pastthe condenser 47 to remove the heat from the chiller 41, and the speedof the impeller may be adjusted. The adjustments to condenser 47, thefan 51 (or impeller), and the compressor 45 are made to alter thecooling power of the chiller 41. Such adjustments may be made in any ofthe manners disclosed in commonly assigned U.S. patent application Ser.No. 62/477,596 filed Mar. 28, 2017, by inventors Gregory Taylor et al.and entitled THERMAL SYSTEM, the complete disclosure of which isincorporated herein by reference. In addition to, or in lieu of, suchadjustments to the compressor 45, condenser 47, and/or fan 51,controller 66 may also be modified in any of the thermal control unitsdiscussed herein to change a flow rate of the circulating fluiddelivered to thermal pads 24.

In any of the embodiments of thermal control unit 22′ discussed herein,controller 66 may also or alternatively be configured to selectivelyopen and close reservoir valve 150 in order to facilitate the cleaningand/or disinfection of thermal control unit 22′. In such embodiments,controller 66 may be programmed to close (and open) reservoir valve 150during routine maintenance of thermal control unit 22′ and/or duringcleansing and/or disinfecting cycles of thermal control unit 22′. Byclosing and opening reservoir valve 150 during a cleansing ordisinfection cycle, cleansing agents within the circulating fluid arenot only carried throughout circulation channel 36 (when valve 150 isopen), but they are also carried through reservoir 32′ (when valve 150is closed). By closing valve 150 for at least a portion of thedisinfection/cleansing cycle, personnel do not need to remove reservoir32′ and clean or disinfect it by hand. Instead, thecleansing/disinfection can be carried out automatically without the userhaving to take any special steps with respect to reservoir 32′. Theselective opening and closing of reservoir valve 150 duringcleansing/disinfection cycles may be carried out in conjunction with anyof the cleansing/disinfection techniques disclosed in commonly assignedU.S. patent application Ser. No. 62/406,676 filed Oct. 11, 2016, byinventors Marko Kostic et al. and entitled THERMAL CONTROL SYSTEM, thecomplete disclosure of which is hereby incorporated herein by reference.It may also be used with still other cleansing/disinfection techniques.

Various other alterations and changes beyond those already mentionedherein can be made to the above-described embodiments. This disclosureis presented for illustrative purposes and should not be interpreted asan exhaustive description of all embodiments or to limit the scope ofthe claims to the specific elements illustrated or described inconnection with these embodiments. For example, and without limitation,any individual element(s) of the described embodiments may be replacedby alternative elements that provide substantially similar functionalityor otherwise provide adequate operation. This includes, for example,presently known alternative elements, such as those that might becurrently known to one skilled in the art, and alternative elements thatmay be developed in the future, such as those that one skilled in theart might, upon development, recognize as an alternative. Any referenceto claim elements in the singular, for example, using the articles “a,”“an,” “the” or “said,” is not to be construed as limiting the element tothe singular.

What is claimed is:
 1. A thermal control unit for controlling apatient's temperature, the thermal control unit comprising: a fluidoutlet adapted to fluidly couple to a fluid supply line; a fluid inletadapted to fluidly couple to a fluid return line; a circulation channelcoupled to the fluid outlet and the fluid inlet; a pump for circulatingfluid through the circulation channel from the fluid inlet to the fluidoutlet; a heat exchanger adapted to add or remove heat from the fluidcirculating in the circulation channel when activated; a fluidtemperature sensor adapted to sense a temperature of the fluid; apatient temperature probe port adapted to receive patient temperaturereadings from a patient temperature probe; a user interface adapted toreceive a patient target temperature; and a controller in communicationwith the patient temperature probe port, the pump, the fluid temperaturesensor, and the user interface, the controller adapted to vary both aflow and temperature of the fluid exiting the fluid outlet in order toautomatically bring the patient to the patient target temperature. 2.The thermal control unit of claim 1 wherein the controller varies a flowof the fluid exiting the fluid outlet by stopping the flow of fluid outof the fluid outlet prior to the patient reaching the patient targettemperature.
 3. The thermal control unit of claim 2 wherein thecontroller monitors a slope of the patient temperature readings for apredefined time period after the flow of fluid out of the fluid outletis stopped, and if the slope of the patient temperature readings changesby more than a threshold during the predefined time period, thecontroller restarts the flow of fluid out of the fluid outlet; and ifthe slope of the patient temperature readings does not change by morethan the threshold during the predefined time period, the controlleractivates the pump and closes a valve such that the fluid circulateswithin the circulation channel of the thermal control unit but does notflow out of the fluid outlet.
 4. The thermal control unit of claim 1further including a fluid reservoir and a valve adapted to selectivelyinclude and exclude the fluid reservoir to and from the circulationchannel, the controller adapted to control the valve in order toautomatically bring the patient to the patient target temperature. 5.The thermal control unit of claim 1 wherein the controller controls theheat exchanger using first and second control loop feedback mechanisms,the first control loop feedback mechanism using a first set ofcoefficients and an error value, the second control loop feedbackmechanism using a second set of coefficients and the error value, theerror value being defined as a difference between a current patienttemperature reading and the patient target temperature.
 6. A thermalcontrol unit for controlling a patient's temperature, the thermalcontrol unit comprising: a fluid outlet adapted to fluidly couple to afluid supply line; a fluid inlet adapted to fluidly couple to a fluidreturn line; a circulation channel coupled to the fluid outlet and thefluid inlet; a pump for circulating fluid through the circulationchannel from the fluid inlet to the fluid outlet; a fluid reservoiradapted to supply fluid to the circulation channel; a heat exchangeradapted to add or remove heat from the fluid circulating in thecirculation channel when activated; a valve adapted to selectivelyinclude the fluid reservoir in the circulation channel and selectivelyexclude the fluid reservoir from the circulation channel, the fluidflowing through the fluid reservoir when the fluid reservoir is includedin the circulation channel and the fluid flowing around the fluidreservoir when the fluid reservoir is excluded from the circulationchannel; and a controller in communication with the pump, the heatexchanger, and the valve, the controller adapted to control the valveand the heat exchanger in order to automatically bring the patient to apatient target temperature.
 7. The thermal control unit of claim 6further comprising a second heat exchanger adapted to add or remove heatto fluid contained within the fluid reservoir such that a temperature ofthe fluid inside of the fluid reservoir can be adjusted independently ofthe fluid outside of the fluid reservoir.
 8. The thermal control unit ofclaim 6 wherein the controller is adapted to control the valve such thatthe fluid reservoir is included in the circulation channel when thethermal control unit is being disinfected.
 9. The thermal control unitof claim 6 wherein the controller is adapted to control the valve incombination with the heat exchanger in order to automatically bring thepatient to the patient target temperature.
 10. The thermal control unitof claim 6 further comprising a patient temperature probe port adaptedto receive patient temperature readings from a patient temperatureprobe, and wherein the controller controls the valve to exclude thefluid reservoir from the circulation channel for an initial periodduring which the patient temperature readings approach but do not reachthe patient target temperature, and the controller controls the valve toinclude the fluid reservoir in the circulation channel during asubsequent period after the initial period, the subsequent periodcommencing prior to the patient temperature readings reaching thepatient target temperature.
 11. The thermal control unit of claim 10wherein the controller varies a flow of the fluid exiting the fluidoutlet by stopping the flow of fluid out of the fluid outlet prior tothe patient temperature reaching the patient target temperature.
 12. Thethermal control unit of claim 10 wherein the controller monitors a slopeof the patient temperature readings for a predefined time period afterthe flow of fluid out of the fluid outlet is stopped, and if the slopeof the patient temperature readings changes by more than a thresholdduring the predefined time period, the controller restarts the flow offluid out of the fluid outlet; and if the slope of the patienttemperature readings does not change by more than the threshold duringthe predefined time period, the controller activates the pump andcontrols the valve such that the fluid reservoir is included within thecirculation channel.
 13. The thermal control unit of claim 6 furthercomprising: a fluid temperature sensor adapted to sense a temperature ofthe fluid; a patient temperature probe port adapted to receive patienttemperature readings from a patient temperature probe; and a userinterface adapted to receive the patient target temperature; and whereinthe controller controls the heat exchanger to automatically bring thepatient to the patient target temperature, and the controller controlsthe heat exchanger using first and second control loop feedbackmechanisms, the first control loop feedback mechanism using a first setof coefficients and an error value, the second control loop feedbackmechanism using a second set of coefficients and the error value,wherein the error value is defined as a difference between a currentpatient temperature reading and the patient target temperature.
 14. Athermal control unit for controlling a patient's temperature, thethermal control unit comprising: a fluid outlet adapted to fluidlycouple to a fluid supply line; a fluid inlet adapted to fluidly coupleto a fluid return line; a circulation channel coupled to the fluidoutlet and the fluid inlet; a pump for circulating fluid through thecirculation channel from the fluid inlet to the fluid outlet; a heatexchanger adapted to add or remove heat from the fluid circulating inthe circulation channel when activated; and a controller incommunication with the pump and the heat exchanger, the controlleradapted to control the heat exchanger in order to cool the patient to atarget patient temperature, the controller further adapted toautomatically pause cooling of the patient prior to the patient reachingthe target patient temperature and assess a reaction of the patient tothe pause in cooling, the controller still further adapted to warm thefluid internally within the thermal control unit if the reactionindicates the patient will likely reach the target patient temperaturewithout further cooling by the thermal control unit and to restartcooling of the patient if the reaction of the patient indicates thepatient will likely not reach the target patient temperature withoutfurther cooling by the thermal control unit.
 15. The thermal controlunit of claim 14 wherein the pause in cooling of the patient prior tothe patient reaching the target patient temperature includes at leastone of the following: deactivating the pump or deactivating the heatexchanger.
 16. The thermal control unit of claim 14 wherein the pause incooling of the patient prior to the patient reaching the target patienttemperature includes keeping the pump activated while closing a valvesuch that fluid does not exit out of the fluid outlet.
 17. The thermalcontrol unit of claim 14 further comprising: a fluid reservoir adaptedto supply fluid to the circulation channel; and a valve adapted toselectively include the fluid reservoir in the circulation channel andselectively exclude the fluid reservoir from the circulation channel,the fluid flowing through the fluid reservoir when the fluid reservoiris included in the circulation channel and the fluid flowing around thefluid reservoir when the fluid reservoir is excluded from thecirculation channel.
 18. The thermal control unit of claim 17 whereinthe controller is adapted to control the valve such that the fluidreservoir is excluded from the circulation channel during cooling of thepatient.
 19. The thermal control unit of claim 18 wherein the controlleris adapted to control the valve such that the fluid reservoir isincluded in the circulation channel when the controller warms the fluidinternally within the thermal control unit.
 20. The thermal control unitof claim 17 further comprising a second heat exchanger adapted to add orremove heat to fluid contained within the fluid reservoir such that atemperature of the fluid inside of the fluid reservoir can be adjustedindependently of the fluid outside of the fluid reservoir.